Why are sunsets red after a volcanic eruption?

Answer 1

When light from the sun passes through a greater thickness of the atmosphere more light from short wavelengths of visible light (blue and violet) is removed by scattering before it reaches your eyes leaving behind long wavelengths of visible light (red and orange) that also reflect off of clouds making them red too, that's what makes sunsets and sunrises red too because when the sun is setting or rising it's light has to pass through more gases in the atmosphere instead of in the afternoon when its high in the sky (blue sky). When volcanic ash is the air it thickens the atmosphere and can be reflected off of the particles.

Answer 2

The debris in the air from the volcano cause the sky to turn red.